This invention relates generally to electrical instruments using LEDs or similar light elements to indicate the operating condition or status of selected functional portions of the instrument, such as whether a particular function of the instrument has been enabled and/or a result determined relating to that function. More particularly, the invention concerns a system for indicating the operating condition of the LEDs and in addition using the LEDs to provide information about the operating condition of portions of the system other than the functional portions normally associated therewith.
In many electrical instruments, such as for example protective relays used for protection of electric power systems, a plurality of lights, frequently LEDs (light emitting diodes), are used on the front panel of the relay to indicate particular fault conditions detected by the relay. A protective relay typically will carry out a number of protection functions, and the LEDs when lit indicate that the particular protection function associated with the individual LEDs has determined that a fault condition exists. Alternatively, the LEDs can be used to indicate when a particular protection function has been enabled within the relay, as opposed to indicating a result of a protection function.
For instance, a particular relay in one functional configuration might be capable of detecting one or more of a plurality of possible fault conditions involving power line current, voltage and frequency values which are out of normal tolerance. When the voltage or current values obtained from the power line are processed and a fault condition determined, output contacts in the relay are energized, which results in a signal applied to a circuit breaker controlling the associated portion of the line on which the fault has occurred. The LED on the front panel associated with the particular fault condition typically is then illuminated, indicating that the relay has in fact made a particular fault determination.
Users of such equipment are often concerned as to whether or not the light elements themselves are operational; a test push button or other device is frequently used to confirm that the individual lights are in fact operating, i.e. properly connected and not burned out. In one arrangement to accomplish such an objective, appropriate commands or test conditions which mimic fault determinations are provided to the relay, typically by a test set, or from a separate PC (personal computer) or similar device.
However, in some situations, it is inconvenient or otherwise undesirable to have a separate test button on the instrument and/or to use a separate test set for the LEDs. In such cases, it would be desirable to have an LED test system which does not use a separate test circuit or apparatus. Also, it would be desirable to increase the functionality of the LED front panel lights, i.e. the LEDs or other light elements could be used to provide information concerning the operation/function of other aspects of the instrument, in addition to their normal function indications.
Accordingly, the present invention includes a system for testing front panel lights on an electronic instrument, the lights being used to indicate the status of selected operational functions of the electronic instrument, comprising: a clock signal available in the apparatus; at least one timer settable to assert when the clock signal reaches a selected time; and means for programming selected front panel lights to illuminate in response to the timer asserting, wherein a failure of one or more lights to illuminate indicates a failure of the lights.
The invention also includes a system for using front panel lights on an electronic instrument, which are normally used to indicate the status of selected operational functions of the instrument, to also indicate the operating state of other aspects of the instrument, comprising: a clock signal available in the apparatus; at least one timer settable to assert when the clock signal reaches a selected time; and means for programming a plurality of selected front panel lights to illuminate in response to the at least one timer asserting, wherein there is a recognizable difference in the illumination of the front panel lights when there is an error in the clock signal.